1. Field of the Invention
The present invention relates to a method of and an apparatus for detecting an end of a reproduction of main data such as music data, which are recorded on an information record medium such as a CD (Compact Disc), on the basis of sub code data, which are also recorded on the information record medium.
2. Description of the Related Art
A CD is recorded with main data such as music data and sub code data, which correspond to the main data and indicate information for controlling the reproduction of the main data such as track number information, music number information, index information, chapter number information, music title information, time information, absolute time information and so on. A CD player detects a beginning of the main data (e.g. the beginning of one piece of music) and an end of the main data (e.g. the end of one piece of music) in accordance with the content of the sub code data. Thus, the CD player can perform a special reproduction such as a random reproduction, a repeated reproduction and a programmed reproduction, such that the next piece of music is searched on the basis of the detection results. Here, in case that a plurality of various pieces of music are recorded on the CD, the main data correspond to each piece of music. In case that a plurality of movements of one piece of music are recorded on the CD, the main data correspond to each movement of music.
The operation in the CD player to detect the sub code data is performed on the basis of a predetermined clock, which may be Generated by a clock Generator in the CD player or which may be Generated by the clock signal recorded on the CD.
However, an external or internal noise may be mixed into the clock of the CD player while the clock is transmitted through a clock transmission line. Especially, in such a reproducing system that a plurality of CD players are provided in one reproducing system and are controlled by a single controller, since the clock transmission line is relatively long, there is a high possibility that the noise is mixed into the clock. When the noise is mixed into the clock, the controller may fail to correctly read the sub code data. When this happens, the operation of the CD player to detect the beginning and the end of reproduction may not be correctly performed. For example, in the special reproduction by use of the sub code data, even if the reproduction is being conducted in the middle of main data, the reproduction may be suddenly stopped in the middle of the main data and the reproduction of the next main data may be suddenly started, since the end of reproduction of main data is erroneously detected on the basis of the erroneously detected sub code data, which is a serious problem in a practical sense.